1. Field of the Invention
This invention relates to a method of preventing corrosion of aluminum alloys and, more particularly, to a method of preventing corrosion of aluminum alloys, which have been coated on semiconductor substrates and dry etched using chlorine-based gases.
2. Description of the Related Art
The dry etching of aluminum or alloys thereof using chlorine-based gases is posing a problem of corrosion of the aluminum or alloys thereof due to residual chlorine component. There is also a recent demand for aluminum alloy leads, which do not only incorporate copper but also use such a barrier metal as TiN or TiW as an inner layer under the aluminum alloy film. Where the barrier metal such as TiN or TiW is provided as an inner layer, corrosion takes place more readily compared to the case of single aluminum alloy layer leads. This means that the former case requires a more complete corrosion prevention measure. Heretofore, there are the following measures against corrosion of aluminum alloys, particularly Al-Cu alloys, having been dry etched using chlorine-based gases.
(1) The resist is removed while continually maintaining a vacuum after the dry etching. This is done by microwave down-flow ashing using a gas containing oxygen (O.sub.2) and carbon tetrafluoride (CF.sub.4).
(2) After the dry etching, a plasma processing is carried out using a fluorine-based gas such as CF.sub.4, SF.sub.6 and CHF.sub.3, as disclosed in, for instance, Japanese Patent Publication No. 12,343/1983.
(3) After the dry etching, a thermal treatment is carried out at a temperature of 270.degree. C. or above, as disclosed in, for instance, Japanese Patent Disclosure No. 58,835/1988.
However, with any of the sole aluminum alloy corrosion prevention measures (1), (2) or (3) as above, the effect of corrosion prevention is insufficient, and it is necessary to carry out right afterwards a wet process using an alkali solution or an acid. In addition, where there is a film as an inner layer under aluminum alloy and the alloy is to be etched using a fluorine-based gas, there is a problem of side etching of TiN or TiW during a corrosion prevention process using a fluorine-based gas. Further, where the semiconductor substrate is heated to 270.degree. C. or above after the etching, hillocks are formed on the aluminum alloy film to deteriorate the reliability thereof.